Insomnia is the most commonly reported complaint (over 90% prevalence) of patients receiving treatment for Posttraumatic Stress Disorder (PTSD). Insomnia is not effectively treated with pharmacologic treatments and there is insufficient information on the effectiveness of behavioral therapy for sleep problems in PTSD. Recent studies have demonstrated the efficacy of Cognitive Behavior Treatment of Insomnia (CBT-I) in a variety of disorders with comorbid insomnia, which include depression, cancer, alcoholism, traumatic brain injury, and chronic pain. This application will examine if Cognitive Behavioral Therapy for Insomnia (CBT-I), developed in subjects with Primary Insomnia, will improve sleep quality in men and women with chronic Posttraumatic Stress Disorder (PTSD) who have received a first line treatment for PTSD but have persistent insomnia as defined by meeting Research Diagnostic Criteria (RDC) for Insomnia Disorder. This application will examine if CBT-I will improve sleep quality in men and women with PTSD and will gather preliminary data on whether such treatment has clinical effects that extend beyond the amelioration of sleep disturbances. We will obtain pilot data to produce an effect size estimate for CBT-I in PTSD and will develop procedures for applying this treatment in a larger randomized clinical trial. The primary objectives are to examine whether an 8 week course of CBT-I compared to a Monitor Only condition produces a significant pre-post decrease in subjective insomnia complaints and improvement in polysomnography sleep continuity in PTSD subjects and to test if the improvement in insomnia is durable. The secondary objectives are to examine whether CBT-I compared to the Monitor Only condition produces a significant pre-post improvement in other clinical outcomes including nightmares, non-sleep PTSD symptoms, mood, daytime vigor, performance on the vigilance testing, and social adjustment. All subjects will be monitored for 1 week with sleep diary, actigraphy, daily measures of fatigue and psychomotor vigilance followed by 2 nights of polysomnography before and after the 8 week treatment or monitor only period. Subjects randomized to CBT-I will have repeat assessments and procedures (except polysomnography) at 6 and 12 months post treatment to test for durability of treatment gains.